I also find that there are taxes that change per vehicle class and going inside allows the attendant to view your vehicle to determine which fuel tax rate to charge. Sometimes you will see this clearer at stations where personal vehicles (including RV's) are fueled at separate diesel pumps from the pumps OTR trucks use. I have also seen (we have it here in AZ) pumps used for fueling only farm, non vehicle equipment, and non-on-the-road construction equipment. So the three separate pump areas all have different prices based on taxes. At stations with fixed price at the pumps, if you use the one with higher taxes you end up paying more for nothing even though you may be in the lower tax bracket. At stations with attendant price input, you may need to go inside if they don't yet have attendant call buttons.